let --maxWorkers accept a percent as value

[capaj]

🚀 Feature Proposal

Let --maxWorkers accept a percent as value. If the remaining value is so small that it only matches less than 1 CPU, always make sure we leave at least 1 core free.

Motivation

We run Jest to test stuff that calls a lot of DB calls. When we keep the default and do not set --maxWorkers we often run into issues where test timeout. This happens because OS is very bad at switching CPU resources from Jest transpiling to database and it basically locks up even the beefiest of machines.
So we need to run jest with a slightly smaller number of --maxWorkers than the host system has available CPU threads. For example

• when running on an OS with 12 CPUs we want to let jest have 10 cores.

• On a system with 4 cpus, we want to let jest have 3 cpus and leave one of the DB.

• On a system with 2 cpus, we want to let jest have 1 cpu and leave one of the DB.

Example

jest --maxWorkers=85%

Pitch

because it is convenient for me and there are other people running into similar issues like for example #8407

[thymikee]

It's already implemented and available in v24.9.0: b644d85

[capaj]

thanks @thymikee, lovely.

[github-actions]

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